Terrible Fuel Economy!

XJay · Dec 30, 2004

I had two exhaust leaks on my '99 Stang when I bought her, the one at the manifold has been repaired, the one in the pipe ( under the middle of the car ) is still yet to be fixed. My mechanic said the first repair should improve the fuel economy, but it still sucks, BADLY........I intend to have a tune-up and the other exhaust leak done, but what else can be done to help my mileage? It's kicking my rear bad.....

ChingonStang · Dec 30, 2004

What kind of MPG are you getting? There are many factors that assist or take away from MPG. Tires, engine tune, air filter, weight, if you run the heater or ac all the time, etc.

Ive never really heard of a small exhaust leak really impacting the MPG. If you say that you need a tune up, then that is probably the main cause.

On my 1996 V6, I can usually go about 346 miles on a full tank.

marvinmycat · Dec 31, 2004

Replace the paper filter with a high flow reusable one.
Clean the MAF sensor, TB, and fuel injectors.
Check the air in the tires.
Get gas from a different gas station and see what happens.
Is it a stick or auto as it could be your dirving on a stick.
Has the car had different gears put in?
Are there any codes being thrown indicating bad O2 sensors or anything else?

doc4444 · Dec 31, 2004

Don't forget the fuel filter. This can reduce gas mileage AND put tremendous wear and tear on your fuel pump if not replaced at correct intervals.

XJay · Jan 7, 2006

Replaced the spark plugs/wires, and have noticed a bit of increase in power, but it seems like the fuel economy just got a bit worse! I checked the air filter, it's okay, I'm about to replace the fuel filter. My tires are never under-inflated, so I know that's not a contributing factor.

Would injector cleaner possibly help?

What about a cold air filter? (I'm thinking, colder air = more air = more burn for less fuel)

Gas is kicking my butt bad here...

BTW, how does one clean the MAF?

b52yellow · Jan 10, 2006

You say "BAD" Gas mileage...what`s that in numbers ????? MPG ?
I just got back from a roadtrip to SAN DIEGO(about 180miles) was driving 80+mph all the way and got 160 miles @ half tank mark....I thought that I was getting a bad gasmileage too, about 15mpg on average but I guess it is just The way you STEP on that pedal........I am driving w/the PEDAL TO THE FLOOR almost all the time...........Did Tune up the vehicle this past Summer though and replaced the Tires 245`s in the back so that takes a bit off the MPG
Also the CHEVRON w/Techron helps alot-I`ve seen a gain when I started using their Gas instead of SHELL`s.
So you can go and TEST your vehicle on the FREEWAY w/cruisecontrol and see what the numbers say........
Good luck

XJay · Jan 24, 2006

How does one clean the MAF sensor? And how much difference could it make, changing the PCV valve?

Skymarshal · Jan 25, 2006

XJay said:
How does one clean the MAF sensor? And how much difference could it make, changing the PCV valve?

The MAF sensor is critical to power and fuel economy, but usually never gets cleaned, since it is upstream from fuel injection, and thus fuel system cleaners.

To clean it, remove the air box from the car, unclip the housing with the air filter, and unsnap the rubber air tube that leads from the MAF to the throttle body (there are some simple snaps on the side. The part that the wiring harness leads into is your MAF housing. Unbolt the two bolts holding it down, and you'll be able to see the sensor wires. DO NOT SCRUB THEM OR TOUCH THEM IN ANY WAY! They are fragile, and if you break one, you get to buy a new MAF ($200). Get some electronic parts cleaner (don't use carb cleaner or brake cleaner) and gently spray the wires until they are clean. Let the assembly air dry, and reassemble. There is a round mesh grille that you can either replace or leave out- it protects the MAF from debris in the air, but there shouldn't be any if you have an air filter. Leaving it out might get you an extra HP or two.

Some people think that running K&N air filters or any oiled cotton filter is bad for your MAF, since the oil mist from a fresh filter will make dust stick that would ordinarily burn off (the MAF wires are heated). K&N swears there's no problem, but it wouldn't hurt to clean your MAF sensor every so often, especially if you run a reusable air filter.

You should also clean the throttle body while you've got the air cleaner assembly off. Make sure the MAF is plugged in so the computer doesn't throw a CEL code, and start the engine. Spray bursts of carb cleaner into the throttle body, revving the engine with your other hand so it doesn't stall. Doing these little things will keep your performance and fuel economy as high as it can be, and might help when it comes time to pass emissions, too!

Engage47 · Jan 25, 2006

+1 i gained 3 MPG city by cleaning the MAF and trottlebody im totaly with Skymarshal on this one!!!!

98CobraClone · Jan 27, 2006

So, has anyone actually seen what he considers "Terrible Fuel Economy"????????????

Won't tell us..........so we can't tell you what to do to improve. Step #1, keep your foot out of it.

But the mileage is just like horsepower. You have to create a baseline to see what you can improve upon.

XJay · Jan 31, 2006

98CobraClone said:
So, has anyone actually seen what he considers "Terrible Fuel Economy"????????????

Won't tell us.....

Perhaps that's because I don't have an exact figure?

So, to satisfy your obvious curiousity, I'll share all that I know on it:

When I first got her in September '04, I could drive down to the coast (about 90 miles) and back, and use little under half a tank. Now, when I make the trip, it takes nearly three quarters of a tank to do the job.

sejinv · Mar 3, 2006

Skymarshal said:
The MAF sensor is critical to power and fuel economy, but usually never gets cleaned, since it is upstream from fuel injection, and thus fuel system cleaners.

To clean it, remove the air box from the car, unclip the housing with the air filter, and unsnap the rubber air tube that leads from the MAF to the throttle body (there are some simple snaps on the side. The part that the wiring harness leads into is your MAF housing. Unbolt the two bolts holding it down, and you'll be able to see the sensor wires. DO NOT SCRUB THEM OR TOUCH THEM IN ANY WAY! They are fragile, and if you break one, you get to buy a new MAF ($200). Get some electronic parts cleaner (don't use carb cleaner or brake cleaner) and gently spray the wires until they are clean. Let the assembly air dry, and reassemble. There is a round mesh grille that you can either replace or leave out- it protects the MAF from debris in the air, but there shouldn't be any if you have an air filter. Leaving it out might get you an extra HP or two.

Some people think that running K&N air filters or any oiled cotton filter is bad for your MAF, since the oil mist from a fresh filter will make dust stick that would ordinarily burn off (the MAF wires are heated). K&N swears there's no problem, but it wouldn't hurt to clean your MAF sensor every so often, especially if you run a reusable air filter.

You should also clean the throttle body while you've got the air cleaner assembly off. Make sure the MAF is plugged in so the computer doesn't throw a CEL code, and start the engine. Spray bursts of carb cleaner into the throttle body, revving the engine with your other hand so it doesn't stall. Doing these little things will keep your performance and fuel economy as high as it can be, and might help when it comes time to pass emissions, too!

Thanks for the great info Skymarshal but I have hit a little snag, the two bolts holding the sensor into the housing are like normal torq screws however they have a bulge in the middle of them preventing me from using any of my normal screwdrivers, did you have to purchase a separate screwdriver for this task or did you use something you had lying around?

Also if I can not remove the actual sensor from the housing, has anyone just sprayed the eletronics cleaner right down the hole, cause you can see the wire sensors and could easily access them that way, but I fear the chemicals may mess something else up with the assembly.

Sejin

Skymarshal · Mar 3, 2006

I just used a Torx bit. If you don't have any, it's worth it to go out and buy a set. You can find a Chinese-made set for around $15. Cars have a lot of them nowdays, and it's worth it to use the right bit so you don't mess the bolt up with a screwdriver.

You really need to take the sensor out to clean it. The MAF wires are in a hood that sticks out into the airflow, and they need to be sprayed directly. Also, if you don't disassemble it all the way, you can't take out that round screen that reduces airflow.

3.9stang · Mar 3, 2006

same problem

I also get horrible fuel economy. My meter said I went around 8 miles in an 1/8 tank. I had 150 miles on a full tank, goin fast on freeways mostly. My gas meter says empty and when I refuel it only put in 12 gallons. I think my car is messed up. Its a 2004 3.9L V6 Mustang. any suggestions?

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